❄️ AC Tonnage Calculator
Estimate the right air conditioner size for your home
🗺️ Climate Zones Reference
Your location significantly affects cooling needs. A 2000 sq ft house in Arizona needs more cooling than the same house in Maine.
- Zone 1 (Very Hot): Florida, Texas, Arizona, Southern California (Need ~1 ton per 450 sq ft)
- Zone 2 (Hot): Georgia, Alabama, Mississippi, Louisiana (Need ~1 ton per 500 sq ft)
- Zone 3 (Moderate): Virginia, Kentucky, Missouri, Kansas (Need ~1 ton per 550 sq ft)
- Zone 4 (Cool): New York, Pennsylvania, Ohio, Michigan (Need ~1 ton per 600 sq ft)
- Zone 5 (Cold): Maine, Minnesota, North Dakota, Canada (Need ~1 ton per 650+ sq ft)
"The most common mistake homeowners make is thinking 'bigger is better.' If you install a 5-ton unit in a house that only needs 3 tons, the unit will cool the air so fast that it shuts off before it has removed the humidity. You end up with a cold, damp, clammy house that smells like mildew. We call this 'short cycling.' It also wears out your compressor faster. Always size correctly, or slightly undersize rather than oversize."
📐 How AC Sizing Works
Air conditioner capacity is measured in BTUs (British Thermal Units) or Tons. One Ton equals 12,000 BTUs per hour.
The Calculation Factors
- Base Load: Square footage × Climate Factor (e.g., 20-30 BTU per sq ft).
- Insulation Adjustment: Poor insulation lets heat in, increasing load by 10-20%. Good insulation reduces it.
- Sun Exposure: West-facing windows add significant heat gain in the afternoon.
- Occupancy: Add ~400 BTU per person (usually negligible for residential unless hosting parties).
- Kitchen: Add ~1,200 BTU if the kitchen is part of the open cooling zone.
Common AC Sizes
| Tonnage | BTU/hr | Typical Area (Zone 3) |
|---|---|---|
| 1.5 Tons | 18,000 | 600 - 900 sq ft |
| 2.0 Tons | 24,000 | 900 - 1,200 sq ft |
| 2.5 Tons | 30,000 | 1,200 - 1,500 sq ft |
| 3.0 Tons | 36,000 | 1,500 - 1,800 sq ft |
| 3.5 Tons | 42,000 | 1,800 - 2,100 sq ft |
| 4.0 Tons | 48,000 | 2,100 - 2,400 sq ft |
| 5.0 Tons | 60,000 | 2,500 - 3,000 sq ft |
⚠️ Common Mistakes
1. Buying based on the old unit size: The old unit might have been sized wrong, or you might have added insulation/new windows since then. Always recalculate.
2. Ignoring ceiling height: This calculator assumes standard 8-9 ft ceilings. If you have 12-15 ft vaulted ceilings, add 10-20% to the tonnage.
3. Not accounting for duct leakage: Leaky ducts can lose 20-30% of your cooling. Sealing ducts is often cheaper than buying a bigger AC.
4. Forgetting internal heat loads: A home office with servers, gaming PCs, and multiple monitors generates significant heat that needs extra cooling capacity.
❓ FAQ
What is a "Ton" of cooling?
It's a historical term. One ton is the amount of heat required to melt one ton (2,000 lbs) of ice in 24 hours. It equals 12,000 BTU/hr.
Can I install a 3.5 ton unit?
Yes, residential central AC units typically come in 0.5-ton increments (1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0). Window units are sized by BTU (5,000 to 24,000).
What if my calculation is between sizes?
If you calculate 2.7 tons, you generally round up to 3.0 tons. However, if you have excellent insulation and low humidity, rounding down to 2.5 tons might provide better humidity control. Consult a pro.